In a paper conveyance apparatus provided in an apparatus such as an image reading apparatus and an image copying apparatus, a jam may occur when a paper moves in a conveyance path. Some paper conveyance apparatuses include a function for determining whether a jam has occurred based on whether a paper has been conveyed to a predetermined position in a conveying path within a predetermined period of time after initiation of conveyance of the paper, and then terminating an operation of the apparatus when a jam has occurred.
Conventionally, there is known a sheet multiple feed detection apparatus that compares ultrasound attenuation information when a paper sheet has passed between a transmitter and a receiver with a threshold value for multiple feed detection to detect sheet multiple feed. A periphery of an ultrasound reception region of the sheet multiple feed detection apparatus is covered with a cylindrical noise shield wall.
There is known an abnormality determination apparatus including a microphone for detecting a sound generated from a subject to be detected and a determination unit for determining the presence or absence of abnormality of a subject to be detected based on a detection result by the microphone.
Further, there is known a multiple feed detection apparatus that transmits ultrasound from a transmitter to a receiver of an ultrasound sensor facing each other across a transfer sheet conveyance path, and compares an output signal by attenuation when a transfer sheet has passed between the transmitter and the receiver with a threshold value for multiple feed detection to detect multiple feed. To prevent disturbance, a cover is disposed on a receiver side of the multiple feed detection apparatus.
In addition, there is known a sheet stacking unit capable of stacking sheets, an optical sensor that detects the presence or absence of sheets stacked in the sheet stacking unit, and a sheet feeding apparatus that separates and feeds sheets one by one by a feeding unit based on a detection result of the optical sensor. A light shield for shielding outside light that enters the optical sensor is provided so as to be withdrawable from a sheet insertion opening of the sheet stacking unit.
Related art is disclosed in Japanese Laid-open Patent Publications No. 2008-207885, No. 2006-201316, No. 2005-82350 and No. 2010-30772.